The pathogenetic mechanisms involved in acute and chronic liver failure are still poorly understood. Currently, abnormalities in the benzodiazepine (BZD) receptor system are widely considered as a mechanism of hepatic encephalopathy (HE). Recent studies in our laboratory suggest that the peripheral-type BZD receptor, which is predominantly localized in astrocytes, may be preferentially involved in HE. This in keeping with substantial evidence indicating that astrocytes are the target cells in HE. Our hypothesis is that toxin-induced abnormalities in the astrocyte BZD receptor are a key factor in the pathogenesis of HE. Since little is known about the significance of the astrocytic BZD receptor, our aim is to investigate its properties and functions in cultured astrocytes. We will determine its intracellular location as this would provide important clues to its function. We anticipate that a major portion will be located on mitochondria an accordingly, we will evaluate the action of BZD on energy metabolism by measuring levels of key energy metabolites and establishing the effect on cellular respiration. Basic cellular effects of BZD on astrocytes including morphology, proliferative capacity, and the status of key astrocytic markers (eg, glial fibrillary acidic protein, glutamine synthetase, pyruvate carboxylase) will be established. As the BZD receptor is also likely to be located in the plasma membrane, the ability of BZD to affect the uptake of cations and neuromodulators will be studied as changes in these properties may affect CNS excitability. The identification of possible second messengers will be done and the effect of BZD on other membrane receptors will be evaluated. The regulatory role of protein phosphorylation in BZD receptor activity, as well as the effect of agents known to modify the BZD receptor in other systems eg, taurine, melatonin and diazepam-binding inhibitor, will be performed on cultures that head been exposed to HE-related toxins and serum form rabbit with fulminant hepatic failure (FHF). Observed differences between toxin-treated and untreated cultures will support our hypothesis. The last phase of our project density of the peripheral BZD receptor will be determined in various models of HE (thioacetamide-induced FHF, ammonia intoxication, portocaval-shunted rats and portocaval-shunted rats challenged with ammonia). The effect of peripheral BZD receptor blockers on the clinical course of experimental HE will also be carried out. We anticipate that these studies on cultured astrocytes and in vivo models will provide a better understanding of the role of the astrocyte receptor in the pathogenesis of HE and may furthermore provide therapeutic measures which may be useful int he management of patients with this disorder.